1. Field of the Invention
This invention relates to a light emitting device and a method for manufacturing the same.
2. Background Art
Demand for light emitting devices is growing in such applications as illumination apparatuses, display apparatuses, and traffic signals. In these applications, high brightness, high reliability, and mass productivity are increasingly required of light emitting devices.
A light emitting layer made of InGaAlP-based semiconductor can provide emitted light in green to red wavelength range. A lattice constant of InGaAlP-based semiconductor has a small mismatch with a lattice constant of GaAs. Hence, use of a GaAs substrate for crystal growth of a multilayer body including the light emitting layer facilitates reducing crystal defects and increasing the reliability.
On the other hand, a bandgap wavelength of GaAs is longer than a wavelength of green to red visible light. Hence, the emitted light is absorbed, which results in brightness decrease. To reduce absorption in the substrate while reducing crystal defects, a wafer bonding process is used to transfer the multilayer body including the light emitting layer onto another substrate. In this structure, the substrate can be made of silicon, and the emitted light can be reflected by a bonding metal layer. This facilitates increasing volume productivity and bonding strength while increasing the light extraction efficiency.
JP-A-2005-109207 (Kokai) discloses an example of a method for manufacturing a light emitting device in which a device substrate and a compound semiconductor layer are reliably laminated via a metal layer. In this example, temperature raising of the wafers is started at a timing lagging behind the start of pressurizing the joined wafers, thereby avoiding cracks around the bonding metal layer.
However, the mass productivity of cutting process for dicing the thick bonding metal layer thus formed is not sufficiently high, and the yield also requires improvement.